1. Field of the Invention
Xanthan gum is a heteropolysaccharide produced as a fermentation product by Xanthomonas campestris, a microorganism causing vascular disease of cabbages, cauliflower, and rutabagas. Its structure consists of a linear backbone of .beta.-(1.fwdarw.4)-linked D-glucose resides (linked as in cellulose), which has three-unit-long side chains appended on alternate residues. D-Mannose residues directly appended to the backbone bear O-acetyl substituents on the C-6 position. Pyruvic acetal, i.e., 4,6-O-(1-carboxyethylidene), substituents are on the terminal D-mannosyl residues of some of these side chains, their frequency of occurrence depending on the bacterial strain and fermentation conditions.
Xanthan gum has condiderable industrial significance and a vast variety of applications as summarized by A. Jeanes in "Applications of Extracellular Microbial Polysaccharide-Polyelectrolytes: Review of Literature, Including Patents," J. Polym. Sci., Polym. Symp. No. 45, pp. 216-221 (1974). The stability of its rheological properties under diverse chemical conditions accounts in part for its versatility. For example, the gum is an effective brine thickener for use in drilling mud compositions and also in the secondary and tertiary recovery of petroleum. A detailed description of its role in oil recovery is given by Wernau in U.S. Pat. No. 4,119,546. With the potential for use of large quantities in this and other fields, there has been some concern as to its effect on the environment. We have observed that the gum is unaffected after exposure for a year or more to laboratory air or for 10 years when stored in nonsterile tightly closed containers. Even when in contact with high concentrations of soil organisms, the heteropolysaccharide may remain stable for as long as a month. Faced with these observations suggesting that xanthan-degrading organisms are not abundant in nature, this invention relates to the identification and isolation of a culture effective for degrading the gum.
2. Description of the Prior Art
While the literature is replete with reports on the production, characterization, properties, and applications of xanthan gum, there is a paucity of information on its biochemical degradation. M. Rinaudo et al. [Chem. Abstr. 92: 176420a (1980)] investigated the mechanism of enzymic hydrolysis by a cellulase. In salt-free solution, a random breakdown of the main chain was observed when the polysaccharide was in the unordered conformation. However, there was no hydrolysis of the more commonly occurring, ordered helical conformation.